An Internet based communication system is generally comprised of a protocol stack of five layers and each protocol layer is configured as illustrated in FIG. 1.
FIG. 1 illustrates an example of an Internet protocol stack, which is generally used.
Referring to FIG. 1, an uppermost layer of the protocol stack is an application layer and serves to support network application such as FTP/HTTP/SMTP/RTP. The protocol stack further includes a transport layer which serves to transmit data between hosts using TCP/UDP protocol, and a network layer which performs setup of a data transmission path from a source to a destination through IP protocol. Furthermore, the protocol stack includes a link layer which serves to perform data transmission and Media Access Control (MAC) between peripheral network entities through PPP/Ethernet protocol, and a lowermost physical layer which transmits data in units of bits using wire or wireless media.
FIG. 2 illustrates an operation of each layer for data transmission, which is generally used.
Referring to FIG. 2, a transport layer of a transmitting side generates a new data unit by adding header information to a message payload received from an uppermost layer, i.e., an application layer. The transport layer transmits the data unit to a lower layer, i.e., a network layer. The network layer generates a new data unit by adding header information used for the network layer to the data received from the transport layer, and transmits the data unit to a lower layer, i.e., a link layer. The link layer generates a new data unit by adding header information used for the link layer to the data received from the upper layer, and transmits the generated data unit to a lower layer, i.e., a physical layer. The physical layer transmits the data unit, which has been received from the link layer, to a receiving side.
A physical layer of the receiving side receives the data unit from the transmitting side and transmits the data unit to an upper layer thereof, i.e., a link layer. The receiving side processes a header added to each layer and transmits a message payload, from which a header has been removed, to an upper layer. Data transmission and reception between the transmitting side and the receiving side are performed through the above procedure.
As illustrated in FIG. 2, for data transmission and reception between the transmitting side and the receiving side, each layer performs control functions such as data addressing, routing, forwarding, and data retransmission by adding a protocol header.
FIG. 3 illustrates a protocol layer model defined in a wireless mobile communication system based on an IEEE 802.16 system, which is generally used.
Referring to FIG. 3, a MAC layer belonging to a link layer may include three sublayers. A service-specific Convergence Sublayer (CS) may convert or map external network data, which is received through a CS Service Access Point (SAP), into MAC Service Data Units (SDUs) which are received by a MAC Common Part Sublayer (CPS). In this layer, SDUs of an external network are classified and a function that associates them to a corresponding MAC Service Flow IDentifier (SFID) and Connection IDentifier (CID) may be included.
The MAC CPS provides a core MAC function such as system access, bandwidth allocation, connection setup, and connection maintenance and receives data which is classified by a specific MAC connection from various CSs through the MAC SAP. In this case, Quality of Service (QoS) may be applied to data transmission through a physical layer and scheduling.
A security sublayer may provide an authentication function, a secure key exchange function, and an encryption function.
The MAC layer provides a connection-oriented service and is implemented by the concept of a transport connection. When a mobile station (MS) is registered in a system, a service flow may be provisioned by negotiation between the MS and the system. If service requirements change, a new connection may be established. The transport connection defines mapping between peer convergence processes that utilize MAC and a service flow. The service flow defines QoS parameters of a MAC PDU that are exchanged in a corresponding connection.
A service flow for a transport connection performs a core role in operating MAC protocol and provides a mechanism for uplink and downlink QoS management. In particular, the service flow may be integrated with a bandwidth allocation process.
In a general IEEE 802.16 system, an MS may have a 48-bit universal MAC address per radio interface. This address uniquely defines the radio interface of the MS and may be used during an initial ranging process to establish a connection with the MS. Since a Base Station (BS) verifies MSs by different IDs of the MSs, the universal MAC address may be used during part of an authentication process.
Connections may be identified by a 16-bit CID. During initialization of an MS, two pairs of management connections (uplink and downlink) are established between the MS and the BS and three pairs including the management connections may be optionally used.
The above-described IEEE 802.16-series standard is completing specification of IEEE 802.16e and is underway under the name IEEE 802.16m. Hereinafter, IEEE 802.16e will be briefly referred to as 16e and IEEE 802.16m will be briefly referred to as 16m, unless confusion would arise.
FIG. 4 is a diagram explaining the structure of a MAC Protocol Data Unit (PDU) specified by the 16e standard, and FIG. 5 is a diagram explaining in detail the structure of a generic MAC header in the MAC PDU shown in FIG. 4.
Generally, a link layer (or MAC layer) and a physical layer, which are located at a second layer or below, differently define protocol according to each system such as LAN, Wireless LAN, 3GPP/3GPP2 or Wireless MAN and a header format of a MAC PDU according to the protocol. A MAC header may include a MAC address of a node or a link address for data transmission between nodes in the link layer and may include header error check and link layer control information.
Referring to FIG. 4, each MAC PDU starts with a MAC header of a certain length. The header is located in front of a payload of the PDU. The payload of the MAC PDU includes a subheader, a MAC SDU, and a fragment. The length of payload information may vary to contain a variable number of bytes. Therefore, a MAC sublayer can transmit various traffic types of an upper layer even without recognizing the format or bit pattern of a message. All reserved fields are set to ‘0’ during transmission and are disregarded during reception.
The MAC PDU may include Cyclic Redundancy Check for error detection. A CRC function may be implemented in a physical layer of an OFDMA system. All reserved fields in the MAC PDU are designated as ‘0’ and are disregarded during reception.
Hereinbelow, one scale of a block indicating a header structure including the structure of FIG. 5 denotes one bit, a horizontal column denotes one byte, and going downward denotes sequential arrangement from a Most Significant Bit (MSB) to a Least Significant Bit (LSB).
Referring to FIG. 5, six subheaders may be used for a MAC PDU together with a generic MAC header. Subheaders for each MAC PDU are inserted to the rear of the generic MAC header. Each field included in the MAC header will be described below.
A Header Type (HT) field represents a header type, more particularly represents whether a corresponding MAC PDU is a generic MAC header which includes a payload at the rear thereof or a signaling header for control such as a bandwidth request. An Encryption Control (EC) field represents encryption control, more particularly represents whether a payload has been encrypted. A Type field represents the presence/absence of a subheader suffixed to the header and the type of the subheader. An Extended Subheader Field (ESF) field represents the presence/absence of an extended subheader suffixed to the header.
A CRC Indication (CI) field represents whether CRC is suffixed to the rear of payload. An Encryption Key Sequence (EKS) field represents an encryption key sequence number used for encryption if the payload is encrypted. A Length (LEN) field represents the length of the MAC PDU. A CID field represents a connection identifier to which the MAC PDU is transferred. A connection is used as an identifier of a MAC layer for data and message transmission between the BS and the MS. A CID serves to identify a specific MS or a specific service between the BS and the MS. A Header Check Sequence (HCS) is used to detect an error of the header. In FIG. 5, a number in parenthesis next to each field name represents the number of bits occupied by each field.
Meanwhile, the IEEE 802.16Rev2/D4 standard specifies the concept of MAC PDU concatenation to simultaneously transmit a plurality of MAC PDUs in uplink or downlink transmission.
FIG. 6 is a diagram explaining the concept of MAC PDU concatenation.
As illustrated in FIG. 6, when MAC PDU concatenation is used, MAC PDUs are distinguished by CIDs. In addition, a MAC management message, user data, and a Bandwidth Request (BR) MAC PDU may be concatenated for simultaneous transmission. Since the respective MAC PDUs are distinguished by the respective CIDs, a reception MAC entity can provide a MAC SDC by recombining one or multiple MAC PDUs with a corresponding MAC SAP.
Although the MAC PDU concatenation described in conjunction with FIG. 6 has an advantage of transmitting the MAC PDUs transmitted to the same MS by concatenation, MAC PDU headers should be attached to all payloads since data transmitted for each connection is distinguished by the MAC PDU headers. Even if this is efficient for optimization for a MAC message, optimization for the MAC header is not achieved.